Add macros usable by the device tree sources to reference the R8A77980
CPG core clocks by index. The data come from the table 8.2e of the R-Car
Series, 3rd Generation User's Manual: Hardware (Rev. 0.80, Oct, 2017),
however I had to add the Z2 clock which is somehow present only on the
figure 8.1e...

Based on the original (and large) patch by Vladimir Barinov.
Signed-off-by: Vladimir Barinov <vladimir.barinov@cogentembedded.com>
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>